In the case of switching devices having a withdrawable design, the power circuit breaker is held in the associated withdrawable-part rack by way of a self-inhibiting displacement mechanism in the operating position. Since the connections of the power circuit breaker are generally arranged on one side, when a power circuit breaker is switched on, a current loop results. If high short-circuit currents occur, the forces of the current loop act counter to the insertion direction and thus attempt to drive the breaker out of the withdrawable part. If the locking by way of the displacement mechanism does not withstand the forces, under certain circumstances the breaker is moved out of the operating position to a greater extent than the laminated contacts of the power circuit breaker engage in the connection rail of the withdrawable-part rack. This leads to a system failure.
The patent specification DE 102 51 002 B3 has disclosed a generic power circuit breaker. In this case, a locking device is actuated by a switch mechanism, in particular by a switching shaft of the power circuit breaker. The locking device includes an actuating element which is arranged such that it is fixed against rotation on the switching shaft and interacts with a locking bolt. The locking bolt is arranged such that it can be displaced axially and is guided by guide rollers. This locking mechanism is very complex in design terms, however.
A further possibility for reducing the current forces on the power circuit breaker is the use of current-limiting power circuit breakers which limit the prospective short-circuit current and thus also the current-loop forces occurring. These devices have only low selectivity, however, i.e. they can only withstand the short circuit for a very short period of time, with the result that downstream switches in a power circuit distribution system do not have the option of switching off before the power circuit breaker.